Carburetor float mechanism



Feb. 17, 1959 c. R. LUNN v 2,873,957

CARBURETOR FLOAT MECHANISM Filed March 21, 1957 INVENTOR cnnuanron maarMncnANrsM `Clarence R. Lumi, Lathrup Village, Michl, assigner to GeneralMotors "Corporation, Eetroit, Mich., a corporation of DelawareApplication March 2l, 1957, Serial No. 647,528 5 Claims. (Cl. 26l-69)The present device relates to a carburetor float mechanism and moreparticularly one in which the float buoyancy is variable in accordancewith certain operating conditions of the engine.

A problem with carburetor float controlled fuel feeding mechanisms hasbeen that the actuation is v unwantedly variable with certain transientvehicle operating conditions such as turning and accelerating. ln'otherwords, when a vehicle is cornering or accelerating the fluid shifts fromone side to the other within the float bowl chamber and in so doingchanges the position of the float so as not to reflect the actual needsof the fuel system. lFor eX- ample, when the vehicle is going around acorner the fuel may shift to one side thereby increasing the buoyantforce acting on the float to shut off the fuel inlet valve and therebystarving the carburetor causing the engine to stutter or failmomentarily for want of fuel.

.This malfunctioning of the float mechanism has been aggravated withnewer type carburetors in which the depth of the oat bowl chamber hasbeen decreased in order to reduce the vertical height of the carburetorconsistent with the lower vehicle profiles which are being Yutilized onpresent day automobiles. With the shallower type float bowl chambers theaction of the float mechanism becomes more critical in that the totalvertical movement of the float is considerably reduced. 'It is,

therefore, imperative that the float mechanism respond accurately to theneeds of the engine and not be unduly shifted by transient operatingconditions. Attempts' have been .made to solve this problem by combiningspring mechanisms with the float member in such a way as to increase thebuoyancy of `the float mechanism. However, suchspring devices havethemselves created certain problems which are equally as undesirable asthe original problem which was sought to be solved.

lt has been found with the type of spring mechanisms utilized heretoforeto increase the buoyancy of the kfloat mechanism that o-n accelerationor high speed cornering such mechanisms enhanced the tendency of Athefloat to shut oifthe fuel inlet valve at a time when large quantities ofVfuel are required.

Y it is the purpose of the presentinvention to 'provide meanswhichfunder normal operating conditions increases the-buoyancy ofthcztioat mechanism to avoid Yflooding of the float bowl chamber.buoyancy increasing means is, however, made responsive to the load onthe engine and rendered inoperative under conditions of high powerdemand.' Under such conditions the lioat mechanism is relatively lessbuoyant which tends to maintain the fuel inlet -valve in an openposition to provide thelrequisite quantity Vof'fuel for high-power isoperative under high engine load conditions to render said deviceinoperative.

ln the present invention the :to the throttle valve 2t?. The idling fuelflow takes place only when the throttle Zo is closed as shown. v

While the main fuel well Sil in combination with the 2,873,957 PatentedFeb. 17, 1959 The details of the present invention as well as otherobjects and advantages will vbe apparent from a perusal of a detaileddescription which follows. y

The drawing is a partially sectioned view of a carburetor embodying thesubject invention.

The carburetor lil on which the subject invention has been embodied isselected Vmerely for illustrative purposes since the present device isadaptable for use with any type of carburetor. Carburetor l@ includes athrottle casing l2, a float bowl casing le and a cover casing lo. Aninduction passage t3 is formed through the casing members and thecombustible charge flow controlled by a throttle valve Ztl disposed inthe throttle casing l2. A fuel chamber ZZ is formed in the float bowlcasing l@ and is adapted to receive fuelfrom an inlet passage 2licontrolled by an inlet valve mechanism indicated generally at 25. Theinlet passage 24 and the inlet valve 2d are formed in or supported fromthe float bowl cover l2. The valve mechanism 2o may be of anyconventional type but in general includes a slidable valve member 2Swhich is adapted to coact with a valve seat 3d formed in the valvebody/'32 to control the Vflow of fuel into the fuel chamber 22 inaccordance with the axial position of the member 25.

A float mechanism indicated generally at .Ts-i is pivoted on a bracket36 supported from the cover l2 and includes the float 38 supported fromthe pivoted arm itil. Arm 'do includes a portion t?. adapted to engagethe slidable valve member 2S and move the latter axially within thevalve casing 32 in accordance with the position ofthe fuel levelcontrolled float member 3S. -As the fuel level in the chamber 22 isreduced the float drops-opening the valve mechanism'ii'o to admit morefuel into the fuel chamber until suchtime as the fuel reaches the properlevel to shut off the valve.

As already noted, with the vehicle accelerating or taliing corners athigh speeds theliuid within the chamber 22 will shift and so actuate thefioat mechanism as not to rellect the actual need of the fuel system.

Main and idling fuel wells Siti and 52 Vare formed in the Vfloat 4bowlcasing ld and are in communication with'each other and with the fuelchamber 22 through a passage 53 including a metering orifice 54. A mainfuel nozzle S6 projects within the main fuel well 5@ and communiidlingfuel well 52 includes an idle fuel nozzle 6b which communicates throughpassage 643 with'the induction passage 18 through an idling orifice o6disposed posteriorly metering orifice 54 is suicient to vprovide fuelfornormal Operating conditions it is inadequate to supply suia passage73.' The power mechanism 7i) includes a vacuum piston 74 disposed in achamber formed in the cover l2 and 'whichpiston is biased in a downwardposition'by a 4spring member 76, which surrounds piston rod 77. Spring76 seats at one'end upon a washer 79 mounted in cover l2 and biases atitsother end against a washer 8l fixed to rod 77. Rod 77 is adapted toengage valve member 72. Valve member 72 is normally biased against itsseat 78 by a spring member Si). Piston chamber 32 is communicatedthrough a port 84 with a vacuum passage 86 connecting with inductionpassage 18 posteriorly of throttle valve to transmit manifold vacuum topiston 74. Under normal operating conditions the manifold vacuum inpassage 86 is suiiicient to maintain the piston 74 in an upward positionagainst the force of spring 76 and in so doing permits the spring 80 toclose valve 72. In this way fuel is supplied to oat chamber 22 bymetering orifice 54 only. When, however, the load on the engine isincreased sufficiently to require additional fuel the manifold vacuum inchamber 82 drops to a value which enables vacuum piston spring 76 tomove the piston downwardly unseating valve 72 and admitting additionalfuel to the main metering well 50 to meet the additional demand on theengine. The mechanism as thus far described is conventional incarburetors as presently manufactured.

As already suggested the present day use of shallower iioat b owlchambers has resulted in a relative decrease in the buoyant forceavailable to act upon the float mechariism, for this reason additionalspring 90 has been provided to supplement the buoyancy of float 38. Thewasher 81 4is suiiiciently enlarged to provide a seat for spring 90which is suitably` fixed thereto. The other end of spring 90 is adaptedto bias against an arm 92 fixed on the float bowl arm 40. Thus, undernormal operating conditions with the power piston 74 in the positionshown `in the drawings, the spring member 90 will exert an additionalbuoyant force on the float mechanism 34 which olfsets the reducedbuoyant iiuid force acting on the fioat 38 due to the use of a shalloweroat bowl S8.

By mounting the spring 90 on a portion of the power mechanism 70 it willhe seen that under high load conditions the spring member will be movedout of engagement with arm 92 thereby eliminating its supplementalbuoyant action on the oat bowl mechanism. This more closely correspondsto the needs of the engine. which under high speed acceleration orcornering conditions must be assured of adequate fuel in the float bowlchamber 22. To illustrate, under accelerating conditions the fuel infioat bowl chamber 22 would tend to move to the rear of the chamber, theright as viewed in the drawing, which had the effect of increasing thebuoyant force acting on the oat 38 and thereby tending to shut off theinlet valve 26 resulting in a starving of the engine for fuel. Thisincreased buoyant effect is, however, compensated for in the presentmechanism by the elimination of the buoyant action of spring 90 whichunder the same accelerating or high load conditions is moved downwardlywith the power piston 74 so as to be out of engagement with the arm 92mounted on oat arm 40. Thus, the iioat valve mechanism will continue toprovide fuel to the float bowl chamber in accordance with the needs ofthe engine notwithstanding high speed acceleration or cornering.

To insure that the spring 90 will not be moved out of operativeengagement with the floatarm 92 by possible rotation of the power pistonmechanism 70 a rod member 94 is fixed to the Washer 81 and is adapted toproject through a suitable hole in the cover 12. In this waysupplemental spring 90 will always be aligned with the float arm 92. Y

I claim:

l. A carburetor mechanism for an internal combustion engine comprising afuel chamber, an induction passage, first passage-means for supplyingfuel to the fuel chamber, a first valve mechanism for controlling the owof fuel from said passage to said chamber, a float mechanism in saidfuel chamber for controlling the actuation of said valve in accordancewith the level of fuel in the oat bowl chamber, second passage means forconveying fuel from the float chamber to the induction passage, a secondvalve for increasing the flow of fuelthrough said second fuel passagemeans, means normally biasing the second valve in a closed position, amanifold vacuum responsive member adapted to unseat the second valve,spring means operatively connected to said member and adapted to engageand increase the buoyancy of the float mechanism under normal engineoperating conditions, and means for shifting said member to open thesecond valve and render the spring means inoperative upon a drop inmanifold vacuum.

2. A carburetor mechanism as set forth in claim l in which said firstand second valve mechanism and said spring means are disposed in saidfuel chamber.

3. A carburetor mechanism for an internal combustion engine comprising afuel chamber, an induction passage, first passage means for supplyingfuel to the fuel chamber, a first valve mechanism for controlling the owof fuel from said passage to said chamber, a oat mechanism in said fuelchamber for controlling the actuation of said valve in accordance withthe level of fuel in the float bowl chamber, second passage means forconveying fuel from the oat chamber to the induction passage, a Sec ondvalve for increasing the iiow of fuel through said second fuel passagemeans, means normally biasing the second valve in a closed position, amanifold vacuum responsive member adapted to .unseat the second valve,spring means operatively connected to said member and adapted to engageand increase the buoyancy of the iioat mechanism under normal engineoperating conditions, means for shifting said member to open the secondvalve and render the spring means inoperative upon a drop in manifoldvacuum, and means for maintaining said spring means in operativealignment with said float mechanism.

4. A carburetor mechanism for an internal combustion engine comprising afuel chamber, an induction passage, first passage means for conveyingfuel from the fuel chamber to the induction passage, second passagemeans for supplying fuel to the fuel chamber, a valve mechanism forcontrolling the flow of fuel from said second passage means to saidchamber, a oat mechanism including a oat arm for controlling theactuation of said valve in accordance with the level of fuel in thefloat bowl chamber, a first spring means adapted to engage said arm forincreasing the buoyancy of the iioat mechanism, manifold vacuumresponsive means normally maintaining said spring means in engagementwith said arm, and a second spring means for shifting the first springmeans out of engagement with said arm upon a drop in manifold vacuum.

5. A carburetor mechanism for an internal combustion engine comprising afuel chamber, an induction passage, rst passage means forv conveyingfuel from the fuel chamber to the induction passage, second passagemeans for supplying fuel to the fuel chamber, a valve mechanism forcontrolling the ow of fuel `from said second passage means to saidchamber, a float mechanism for controlling the actuation of said valvein accordance with the level of fuel in the fioat bowl chamber, engineload responsive means associated with said fuel chamber, and a resilientconnection between the load responsive means and the oat mechanismenabling the resiliency of said connection to be varied with variationsin engine load.

Gilbert Feb. 8, 1944 2,448,709 Gilbelf Sept. 7, 1948 2,692,766 Carlsonet al Oct. 26, 1954

